The objective of this project is to isolate, characterize and determine the mechanisms of action of certain factors, present in serum, that are required for growth and cell division of mammalian cells. Two major lines of work are anticipated during the coming year. One is the study of the properties of isolated membrane vesicles and the interaction of such vesicles with growth factors. Second is the identification of the factors involved in density dependent regulation of growth of BSC-1 cells. Density dependent regulation of growth of these African green monkey kidney cells appears to involve somewhat different serum factors than those involved with mouse embryo 3T3 cells. BIBLIOGRAPHIC REFERENCES: Holley, Robert W. (1975) Factors controlling the growth of 3T3 cells and transformed 3T3 cells. In: Proteases and Biological Control, Cold Spring Harbor Laboratory, pp.777-784. Holley, Robert W., and Trowbridge, Ian S. (1975) Control of growth of mammalian cells. In: Molecular Approaches in Immunology, Academic Press, New York, pp. 289-301.